Resistivity meter



De. 27, 1938. E E BLQNDEAU 2,141,590

RESISTIVITY METER y 1 Filed 061;. 50, 1957 wy @a |A @ik E 1NVENTOR. 75

ATTORNEY 5 Patented Dec. 21, 193s UNITED STATES Geop hysieal Research corporation, N man,

N. Y., a corporation of New Jersey Application Octoim' 30, 1937, Serial No. 171,@22

ing equation:

where pa=apparent resistivity e=potential diierence between the second 20 pair of electrodes.

i=exciting current.

Ic=numerical factor dependent upon the geometrica! arrangement of the four electrodes.

An object of this invention is a device which obviates the necessity of simultaneously measuring the current flow and potential di'erence and gives a. direct reading of the quantity In an apparatus embodying the invention, means are provided for producing current flow in the earth, the resistivity oi' which is to be measured. Also, in the earth are 'provided a pali" of electrodes and the apparatus includes means for comparing the potential produced between said electrodes by the current ilowing through' the earth with a potential produced `by the current in the exciting circuit external to the earth. From such comparison is obtained a direct reading of a quantity which is directly proportional to the earths resistivity.

Other objects, novel features and advantages o! this invention will become apparent from the following specification and accompnng drawings wherein the single ligure illustrates diagrammatically one embodiment of the invention.

A battery l has one terminal connected to an electrode Il set into the earth and has its other terminal connected through a variable and accurately calibrated resistance I2 with a second electrode I3 also set in the earth. A doublethrow, double-pole switch I4 has a pair of statlonary contacts II, one of which is directly (ci. irs-ies) connected to one end oi the resistance l2 while the other contact is connected through the primary of a transformer i@ with the remaining termiual of the resistance. The secondary of the transformer it is included in the input circuit of d a vacuum tuhe amplier i'i in the output circuit of which is arranged a pair of ear phones I8. The switch it has a second pair of stationary contacts i9, one of which is connected to an electrode 2d and the other of which is connected i@ to an electrode di, both of said electrodes being set into the earth. The switch further has a pair of movable contacts 22 which are selectively engageable either with the contacts i5 or with the contacts i9 and between the contacts 22 is connected a condmser it.

In the use of the above-described apparatus to determine earth resistivity, the switch M is operated to bring the contacts 22 into engagement with the contacts i@ thereby charging the @0 condenser to the potential produced between the electrodes 2d and di by the current flow through the earth between electrodes ii and I3. The switch is then thrown to bring the contacts 22 into engagement with the contacts l5, thus con- 25 nectlng the charged condenser across the resistance l2 and the primary of transformer i6. The potential drop across the resistance i2 is 1R where i is the current flowing in the exciting circuit and R is the numerical value of the resistance i2. Ii the potential to which the condenser is charged is greater than iR then the condenser will partially discharge through the primary of transformer it and the momentary ow oi' current thus produced will give a click 35 in the ear phones it. Conversely, if the potential across the condenser is less than iR, then a momentary current will now in the opposite direction through the transformer primary, thus producing a click in the ear phones. By adjust- 40 ing the resistance i2 to make R drop across the resistance l2 exactly equal to the potential of they condenser no click will be heard in the ear phones when the charged condenser is connected across the resistance i2. When this conditionisobtainedthevalueoitheresistance I2 isameasureoftheearthresistivity. The value of the condenser 28 is not critical, but the larger it is made. the greater is the sensivity of the system. For most purposes, it may be of the order of two microtarads. 'Ihe length oi' time during which the condenser must be connected to the electrodes 2l and 2l is not critical but it must be longer than the time constantofthecircuitincludingthecondenserand the electrodes 2d and 2i. The switch may be operated either mechanically or manually and in place of the ear phones may be used any suitable electrical means for producing an audible or visible signal.

It is to be unders that various modications may be made in the device above described Within the scope of the invention as defined in the appended claims. For example, a voltage divider may be substituted for the resistance i2 in which event, there will he no changev in the value oi the exciting current but there will be variation in the potential drop with which the voltage between electrodes 2@ and 2i is comed. K

I claim:

1. A resistivity meter comprising an exciting circuit for producing current fow in the earth, a resistance element in said circuit, a pair of electrodes in contact with Athe earth, a condenser, means for charging said condenser to the potential produced across said electrodes, and means for comparing the potential of the charged condenser with the potential drop vacross said resistance element.

2. A resistivity meter comprising an exciting circuit for producing current iiow in the earth, a variable resistance element in said circuit, a pair of electrodes in contact with the earth, a condenser, means for charging said condenser to the potential across said electrodes, means for adjusting the potential drop across said resistance element to a value equal to the potential of the charged condenser, and means for indicating equality of said potentials.

3. A resistivity meter comprising a source ci electrical current, a pair of electrodes connected to the terminals of said source, a variable resistance between one electrode and one terminal, a double-pole, double-throw switch having a rst and a second pair of stationary contacts and a pair of movable contacts selectively engageable with said stationary contacts, an electrical indicator connected between one terminal of said resistance and one contact of said yfirst pair and the other contact of said first pair being connected to the remaining terminal of said resistance, a condenser connected between said movable contacts, and a second. pair of electrodes y connected to said second paix-of xed contacts.

4. A resistivity meter comprising 'an exciting circuit for producing current flow in the earth, a resistance element in said circuit, a pair of electrodes in contact with the earth, a condenser, means for charging said condenser to the potential produced across said electrodes, an electricalindicator, and means vfor connecting the charged condenser and indicator in series across said resistance.

V5. A resistivity meter comprising an exciting 4circuit for producing current flow in the earth, a

resistance element in said circuit, a pair of electrodes in contact with the earth, a condenser, means for charging said condenser to the potential produced across said electrodes, current responsive means, and means for connecting the charged condenser and current responsive means in series across said resistance.

6. A resistivity meter comprising an exciting circuit for producing current ilow in the earth, a

, resistance element in said circuit, a pair of electrodes in contact with the earth, a condenser, means for charging said condenser to the potential produced across said electrodes, audible signal producing means, and means for connecting the charged condenser and audible signal producing means in series across said resistance.

7. A resistivity meter comprising an exciting circuit for producing current now in the earth, a resistance element in said circuit, a pair of 'electrodes in contact with the earth, a condenser, means for charging said'condenser to the potential produced acrossv said electrodes, a voltage detector, and means for connecting the charged condenser and voltage detector in series across said resistance.

f 8. A resistivity meter comprising a -sourcey of electrical current, a pair of electrodes connected to the terminals of said source, a variable resistance between one electrode and one terminal,

a double-pole, double-throw switch having a firstv and second pair of stationary contacts, and a pair of movable contacts selectively engageable with said stationary contacts, a voltage detector yconnected between one terminal of said resistto said pair of fixed electrodes.

9. A resistivity meter comprising a source of electrical current, a pair of electrodes connected to the terminals of said source, a variable resistance between one electrode and one terminal, current responsivemeans, a second pair of electrades, a condenser, 'and means for selectively connecting said condenser in series with said second pair of electrodes and in series with said current responsive device across said resistance.

10. A resistivity meter comprising a source of electrical current, a pair of electrodes connected to the terminals of said source, a variable resistance between one electrode and one terminal, audible signal producing means, a condenser, and means for selectively connecting said condenser in series with said second pair of electrodes and in series with said signalling means across said resistance..

ERNEST E. BLONDEAU. 

